feat(ui): implement premium mobile-first reader toolbar, bottom navigation, and auth ux stabilization (#61)

# Description

This Pull Request integrates the premium mobile-first layout enhancements, a responsive, full-bleed Reader Toolbar, and critical authorization flow stabilizations for the NexusReader Blazor application (targeting .NET 10 with Native AOT compatibility).

Resolves #62
Resolves #63
Resolves #15

## Key Changes

### 📱 1. Mobile-First Reader Layout & Toolbar
- **Full-Bleed Responsive Layout**: Redesigned `ReaderLayout` to feature a premium mobile-first three-tab bottom navigation system (Chapters, Graph, Assistant) and a glassmorphic floating action button (FAB) for the AI assistant.
- **Header & Escaping Routes**: Built `MobileReaderToolbar` with seamless exit paths back to the "Pulpit" (dashboard) and smooth transitions.
- **Custom Iconography**: Added the custom `NexusIcon` component supporting dynamic theme styling and responsive layouts without relying on external CSS frameworks.

### 🔐 2. Authentication Flow UX Stabilization
- **WASM Transition Hydration**: Implemented `AuthenticationStatePersister` and loading preloaders to eliminate authorization race conditions during Blazor WASM interactive hydration.
- **AOT-Compatible JWT Validation**: Integrated a robust, AOT-compatible `JwtTokenValidator` with unit tests (`JwtTokenValidatorTests.cs`) to cleanly parse claims without throwing performance-heavy runtime exceptions.
- **Secure Header Propagation**: Standardized token transmission in WASM (`AuthenticationHeaderHandler.cs`) and MAUI Hybrid client layers (`MobileAuthenticationHeaderHandler.cs`), ensuring cookies are correctly propagated.

### 📊 3. D3.js Knowledge Graph & Interaction
- **Dynamic Viewport Synchronization**: Refactored `knowledgeGraph.js` to ensure the SVG graph behaves correctly under flexbox containment, handles panel expansion/collapse gracefully, and avoids infinite loop redraws.
- **Interaction Hook**: Connected graph node clicks directly to chapter jumps via a new `IReaderInteractionService` abstraction.

### 🏗️ 4. Infrastructure & Central Package Management (CPM)
- **Beta Deployment Configuration**: Added `.env.test.template`, `docker-compose.test.yml`, and `appsettings.Test.json` with hardened environment security guards.
- **Docker-Compose Cache Optimization**: Maintained CPM consistency during multi-stage Docker builds.

## Verification & Build Results
- Run a successful local build check:
  ```bash
  dotnet build NexusReader.slnx --no-restore
  ```
  **Status**: Successfully completed with `0` compilation errors.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #61
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.UI.Shared/wwwroot/js/knowledgeGraph.js

@@ -200,6 +200,9 @@ export function mount(containerId, data, dotNetHelper) {
     width = container.clientWidth || 400;
     height = container.clientHeight || 400;
 
+    // Clean up any existing SVG to prevent duplicates
+    container.querySelectorAll("svg").forEach(el => el.remove());
+
     // Create SVG
     svgElement = d3.select(container).append("svg")
         .attr("viewBox", [0, 0, width, height])